PASADENA, Calif. — Long known for its Sunday night cartoons headlined by “The Simpsons,” Fox is planning to offer new animated material late on Saturday nights and on an experimental new digital channel.

The network said Sunday that the new effort will be led by Nick Weidenfeld, the former head of program development for the Cartoon Network’s Adult Swim series. The cable network has run a popular series of late-night cartoons on weekdays that has successfully reached a young male audience that TV executives consider valuable and elusive.

Saturday’s 90-minute cartoon block would begin at 11 p.m. ET. Fox hasn’t programmed aggressively in late nights and hopes the new series will provide some competition for NBC’s “Saturday Night Live,” said Kevin Reilly, Fox entertainment president. It will start in January 2013.

Reilly, during a news conference, offered hints but left an air of mystery around the future of some popular Fox prime-time shows like “House,” “Glee,” “Fringe” and “Terra Nova.”

Fox appreciates its Sunday cartoons like “The Simpsons,” which will soon air its 500th episode. But success there left relatively little room for experimentation.

“There has been a lot of talent and a lot of product that we’ve wanted to pursue over the years that did not fit the prime-time mold,” Reilly said.

The digital channel would be available online, through cable on demand, as mobile applications and on game consoles, and it’s somewhat experimental, Reilly said. It would allow Fox to take chances on programming of different lengths, he said.

Reilly conceded he’s put off some decisions on prime-time shows that have doubts about their future. One is the long-running medical drama “House,” which Reilly said months ago was probably in its last year. He said he will meet soon with the show’s producers to decide; he did say it’s very unlikely any of the show’s characters would be spun off into a new series.

He praised producers of “Fringe” for helping Fox drum up some interest in its Friday night schedule. But he noted the show is expensive to produce and at its current ratings, it’s a money-loser for the network.

The prehistoric adventure series “Terra Nova” is doing moderately well, but Fox had been hoping for more. Reilly said the show has struggled creatively in its first season and will face tough competition for a time slot.

“If we had more holes on our network, we would be thrilled to lock that in,” he said. “We’re going to decide very soon.”

“Glee” will be back next season, despite some early ratings troubles, he said. The current high school students will be graduating, said Reilly, who left unanswered how many of those cast members will be returning.